It is proposed to continue the development, evaluation, and implementation of the INTERNIST computer-based diagnostic system for internal medicine developed at the University of Pittsburgh. This resource will provide users with on-line access to an extensive medical data base encompassing more than 500 diseases and three thousand manifestations of disease, which can be used for educational purposes as well as diagnostic consultation. The diagnostic system itself is based on a heuristic 'problem-formation' procedure which has demonstrated capability for solving complex clinical problems involving multiple disease.